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Thread: Shaft Alignment

  1. #1

    Shaft Alignment

    1978, 53' YF, DD 8V71-TI's. Both engines/shafts need alignment. Appears as if the rear motor mounts are hard mounted without any means to adjust them.

    I'm guessing the mounts have to be unbolted and the rear of the engine lifted to put shim material under the mount.

    Does anyone have experience how to align the shafts with this configuration?
    Tim

    Ex 1978 53' YF owner

  2. #2

    Re: Shaft Alignment

    Does your mount look like these? These are shimmed. If you have the rubber jobs, you are SOL ! I just rebuilt and re-aligned my MH20 Allison w/12-71Ns
    last year. Let me know if you need the "dissertation". ws
    Last edited by yachtsmanbill; 03-10-2009 at 05:55 PM.
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
    Uncensored, no nonsense boating fun for adults

  3. Re: Shaft Alignment

    How do you know they need realignment??

    Often there IS more weight on the rear than forward engine mounts and as a result the rear mounts may well be low....but you can't assume that...you must remove each shaft flange, port and stbd, from the transmisson flange and check top and bottom, left and right...four points with a feeler gauge....then rotate the shaft 1/2 turn and repeat.....ideally you will measure identical differences among the four measures....the absolute values are immaterial as they depend on how close you manually place the two flanges....differences should be within a ...two or three thousandths should be good....it depends on the flange diameter....whether you raise the back or lower the front mount shims depends on the center alignment of the two flanges...just hope you don't also have to move the engine left or right....lots of older Hatt engine mounts are adjusted via shims...thin metal pieces that are inserted to adjust the mounting height between the engine mount and engine bed stringers....often you can lift the engine ata mount after loosening all four engine mounts and using a long pry bar with wooden pivot point...otherwise an A frame and lifting chains are ideal....
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  4. #4

    Re: Shaft Alignment

    Mike P
    San Miguel de Allende, Mexico; Kent Island MD; San Antonio TX
    1980 53MY "Brigadoon"

  5. #5

    Re: Shaft Alignment

    Post some pics of your engine mounts and engine beds. Take pics of both front and rear. There are different setups depending on year, model and engines. I'm thinking you probably have the rubber mounts and hopefully the adjustable engine beds. The rubber mounts sag over time but can be fixed if not too far gone. They can be replaced but the cost is outrageous. Post some pics, I'm sure someone will have the answers you need.
    Jack Sardina

  6. #6

    Re: Shaft Alignment

    Thanks everyone for the replies.

    To answer a few of the questions:

    REBrueckner
    How do you know they need realignment??

    >>The reason I think they need to be adjusted is I see the shaft log (both engines) wobbling at speeds from idle on up. I can also feel the misalignment with either engine out of gear.

    When I purchased the boat, 2 years ago next month, we had the props tuned (propscan technique) as well as had both cutlass bearings both (P&S) replaced.

    Here are a couple of pictures. First one is the starboard engine, aft, port mount. The other is the same engine, starboard aft mount.
    Attached Images
    Tim

    Ex 1978 53' YF owner

  7. Re: Shaft Alignment

    If they're WOBBLING there's a decent chance the shaft is BENT.

    Alignment should be checked but its odds on you've got a bent shaft if you can see visible runout during operation.
    http://www.denninger.net - Home page with blog links and more
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  8. #8

    Re: Shaft Alignment

    Shafts are not bent. They were checked when we replaced the cutlass bearings.
    Tim

    Ex 1978 53' YF owner

  9. #9

    Re: Shaft Alignment

    With the Allison gears and couplings, the shaft end is a tapered unit... maybe the taper isnt seated square... that would cause the wobble. I would pull the couplings and clean and inspect, then go from there.
    How do you feel the mis-alignment when in neutral? ws
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
    Uncensored, no nonsense boating fun for adults

  10. #10

    Re: Shaft Alignment

    You may have a bad output bearing on the gears. Very common problem on the old Allison M gears. Split the shaft coupling from the gear to check the allignment. Then check to see if there is play on the output flange of the gear. There should be slight movement fore and aft, but if you can move them up and down or side to side, you have a problem with the gear. Fix that first since the gear has to come out. You'll have to realign once the gears go back in.
    Jack Sardina

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